Defrost timers are used to control defrost heaters in freezers and refrigerator/freezers. While their application is mainly for commercial applications, many higher-end consumer refrigeration appliances also now include such defrost timers. The defrost heater prevents excessive ice build up on the evaporator coil to prevent cooling inefficiency in the refrigeration system.
In operation, the defrost timer initiates a defrost cycle after a preset compressor run time. Such compressor run times are selected based on experience with the icing phenomenon for a particular model, installation, etc. That is, it is know that a certain degree of icing on the evaporator coils is likely to have formed once the compressor has been run for a particular length of time. After such icing has likely occurred, the defrost timer initiates a defrost cycle to clear the ice from the coils to maintain the cooling efficiency of the system. The defrost timer also controls the length of the defrost cycle. The length of the defrost cycle is also preset based, once again, on typical icing conditions. That is, the defrost cycle is run for a period sufficient to remove the ice from the coils that has developed during the compressor run cycle.
As is well known, during a typical compressor operation the evaporator fan is running to circulate air over the chilled evaporator coils to cool the chamber. Unfortunately, current defrost timers operate to initiate a defrost cycle immediately after the compressor run cycle has terminated. This results in additional energy usage by the defrost heater because it has to overcome the cooling effects of the just-terminated cooling cycle. That is, immediately after the cooling cycle has ended, and for some period thereafter, the evaporator coils are still very cold from the evaporation of the coolant therein. At least until the evaporation of the coolant in the evaporator has ended, the application of energy to the defrost heater will have little effect to defrost the coils. As such, the defrost heater is simply wasting energy without effect.
There exists, therefore, a need in the art for a new and improved defrost timer that provides adequate defrosting of the evaporator coils of a refrigeration system without consuming excess energy without effect.